SOG coated apparatus to solve SOG non-uniformity in the VLSI process

ABSTRACT

An apparatus for applying spin-on-glass material to a wafer under controlled humidity conditions is described, The apparatus comprises a treatment chamber. Within the treatment chamber are a spin-on-glass coater spin table, a plurality of hotplates connected to one another and from the coater spin table by a moving belt, and wafer handlers to transfer wafers onto the coater spin table and onto the moving belt. A dehumidifier is disposed on top of the treatment chamber and a humidity control unit is disposed on top of the dehumidifier through which air is drawn and whereby relative humidity within the treatment chamber can be controlled.

This is a divisional of application Ser. No. 08/094,705, filed Jul. 22,1993, now U.S. Pat. No. 5,371, 046.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of planarizing an integrated circuitdevice, and more particularly, to a method of planarizing a submicronintegrated circuit device which avoids spin-on-glass non-uniformitydefects.

2. Description of the Prior Art

As devices shrink to the submicron level, interconnects between thesedevices become finer. Planarized dielectric film must be formed betweenthe metal layers of an integrated circuit in order to achieve goodmetallization step coverage of the fine interconnects. Spin-on-glass hasbeen used widely for the dielectric film after its curing to siliconoxide. The material to be applied is thoroughly mixed in a suitablesolvent. The spin-on-glass material suspended in the vehicle or solventis deposited onto the semiconductor wafer surface and uniformly spreadthereover by the action of spinning the wafer. The material fills theindentations in the integrated circuit wafer surface, that isplanarization. Most of the vehicle or solvent is driven off by a lowtemperature baking step often followed by vacuum degassing. Othercoatings of the spin-on-glass material may be applied, baked and vacuumdegassed until the desired spin-on-glass thickness layer is formed. Thefinal step in the making of the spin-on-glass layer is curing. Curing isa high temperature heating step to cause the breakdown of thespin-on-glass material to a silicon dioxide like cross linked material.

Serious non-uniformity defects can be inspected after the second coatingof the spin-on-glass material if the first coating was not cured priorto the application of the second coating. The non-uniformity appearsespecially on bond pads, guard rings, and thin metal lines. The rootcause of the non-uniformity is that the first coated film reactsinsufficiently with the surface of the underlayer, usually aplasma-enhanced silicon oxide. There are two possible solutions to thenon-uniformity problem. The first solution is to cure the firstspin-on-glass layer before the second layer is applied, and then to curethe second layer after it is deposited. The drawbacks of this solutionare that it is too costly and time consuming. The second solution iscompletely unexpected and is the subject of the present invention. Thesolution is to apply the spin-on-glass material under a low relativehumidity process.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide an effectiveand very manufacturable method of planarizing a submicron integratedcircuit wherein there are no non-uniformity defects in the planarizationlayer.

In accordance with the object of this invention, a new method ofplanarizing an integrated circuit is achieved. A first coating of asilicate spin-on-glass material is applied to the surface of a patternedconductor layer to be planarized. The spin-on-glass material is appliedunder low relative humidity, filling the valleys of the irregularstructure of the conductor layer. The first spin-on-glass layer iscovered with a second coating of the spin-on-glass material also appliedunder low relative humidity. Then, both first and second spin-on-glasslayers are cured. This method provides a uniform spin-on-glassdielectric layer upon which a second conductor layer may now besuccessfully applied.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings forming a material part of thisdescription, there is shown:

FIG. 1 schematically illustrates in cross-sectional representation aspin-on-glass machine and dehumidifier used in the present invention.

FIG. 2 schematically illustrates in cross-sectional representation aspin-on-glass coating apparatus enclosed by a humidity controllerchamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now more particularly to FIG. 1, there is shown anillustration of a spin-on-glass machine 1. The machine is within astainless steel chamber 2 with glass panels 4 above. Wafers are loadedinto the chamber at 6 and removed at 8. The wafers are loaded one at atime by the wafer on-load handler 12 onto the coater-spinner table 10.The dehumidifier 22 is shown on top of the spin-on-glass chamber. Thecontrol panel of the dehumidifier is next to the chamber, not shown. Air26 flows into the top of the humidity control unit 24 which keeps theair at a critical relative humidity of less than 35%. A relativehumidity of 30% or less is preferred. Spin-on-glass cracks will be founddue to a too low relative humidity, on the order of 10%. However,surprisingly, it has been found that the critical relative humiditylevels will prevent the formation of cracks in the spin-on-glass. Thetypical fabrication factory ambient relative humidity is about 45% plusor minus 5%, so the relative humidity of the process must be positivelycontrolled using, for example, the dehumidifier.

A silicate spin-on-glass material coats the wafer on the coater/spinnertable 10. It has been found that siloxane spin-on-glass material is nothelped by the low relative humidity of the present invention. Inexperimentation, it has been discovered that a double coat of silicatespin-on-glass in excess of 6000 Angstroms in thickness will show signsof cracking. Therefore, each coating of silicate spin-on-glass must beless than about 2800 Angstroms.

After coating and spinning the spin-on-glass material on the wafer, thewafer off-load handler 14 removes the wafer from the plate 10 and loadsit onto the moving belt 16. The wafer travels to the three hotplates 18,19, and 20 in order for the baking step. The wafer remains on eachhotplate for about 60 seconds. The temperatures of the hotplates areabout 75°-85°, 145°-180°, and 215°-275° C., in order.

The wafer is removed from the spin-on-glass machine and cooled for aboutan hour, then loaded again onto the coater/spinner table 10. A secondcoating of silicate spin-on-glass is applied. The wafer is spun and sentto the hot plates again for the baking of the second layer. The wafer isremoved from the spin-on-glass machine and cured in a 420° C. furnace.

An alternative to the humidity controlled spin-on-glass machineillustrated in FIG. 1 is that illustrated in FIG. 2. Here, the humidityis controlled only when the wafer is on the coater/spinner table 10. Drynitrogen gas 13 is flowed into the enclosure 11 to keep the relativehumidity at less than the critical 35%, and preferably 30% or less. Thisis not a good pattern of gases as is the first embodiment of FIG. 1,because the pattern of gases will influence the uniformity of the liquidpattern. A laminar air flow and dehumidified air could be used as in thetotal environment alternative of FIG. 1.

The spin-on-glass reaction can be characterized as follows: ##STR1## Inthe low relative humidity environment of the present invention, thewater byproduct of the reaction is decreased.

Table 1 compares the results of the low humidity process of the presentinvention to the double cure process of an alternative solution to thenon-uniformity problem.

                  TABLE 1                                                         ______________________________________                                                    Low Humidity Double Cure                                          ______________________________________                                        non-uniformity                                                                              ok             ok                                               thermal budget                                                                              only one 420° C. cure                                                                 cure twice                                       enhance metal-1 void                                                                        better         worse                                            contact spiking                                                                             better         worse                                            cost          low            high                                             cycle time    shorter        longer                                           ______________________________________                                    

A greater thermal cycle will improve the metal-1 void and contactspiking. In the case of the double cure, the additional thermaltreatment for the additional cure will deplete the thermal budget forthe backend process. Thermal budget is defined as the amount of heatthat can be used during a process (such as the backend process) withoutcausing the devices of the integrated circuit to go out of specificationdue to the movement of dopants during the heating steps.

Both the double cure process and spin-on-glass coating in low humiditycan solve the spin-on-glass non-uniformity problem. Spin-on-glasscoating in low humidity has the advantages over the double cure processof lower cost, shorter cycle time, more backend thermal budget, andsimple operation.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of the invention.

What is claimed is:
 1. An apparatus for applying spin-on-glass materialto a wafer under controlled humidity conditions comprising:a treatmentchamber; a spin-on-glass coater spin table within said treatmentchamber; a plurality of hotplates within said treatment chamberconnected to one another and from said coater spin table by a movingbelt; wafer handlers within said treatment chamber to transfer wafers,onto said coater spin table and onto said moving belt; a dehumidifierdisposed on top of said treatment chamber; and a humidity control uniton top of said dehumidifier through which air is drawn and wherebyrelative humidity within said treatment chamber can be controlled.
 2. Anapparatus for applying spin-on-glass material to a wafer undercontrolled humidity conditions comprising:a spin-on-glass coater spintable; an enclosure completely covering said coater spin table; adehumidifier incorporated with a top of said enclosure; and a humiditycontrol unit disposed on top of said dehumidifier through which air isdrawn and whereby relative humidity within said enclosure can becontrolled to less than about 35%.
 3. An apparatus of claim 13 whereinsaid humidity control unit further comprises means for flowing drynitrogen gas into said enclosure until desired relative humidity isachieved.